Epidermal growth factor receptor (EGFR), a transmembrane tyrosine kinase receptor that is overexpressed in many epithelial tumors, including colorectal and head and neck cancers. Upon binding to its natural ligands (e.g., EGF, TGF-α), EGFR forms homodimers or heterodimers, triggering intracellular tyrosine kinase activation and downstream signaling cascades (such as RAS-RAF-MAPK and PI3K-AKT pathways) that promote cell proliferation, survival, angiogenesis, and metastasis.